1. Field of the Invention
The present invention relates to a simulation method for estimating the performance of a product made of a viscoelastic material. More particularly, the present invention relates to a simulation method for accurately estimating the performance of the product made of the viscoelastic material by means of a simulation.
2. Description of the Related Art
A viscoelastic material represented by a macromolecular material such as rubber or elastomer is widely applied to various products such as tires, balls for sports, rolls for printing machines.
It is expensive and takes much time to make a trial manufacture. Thus to save cost and time, simulation is made in various industrial fields to develop various products made of the viscoelastic material or a metal material. For example, to estimate the restitution performance of a golf ball, simulation methods of actual hitting tests are proposed.
To conduct the simulation, physical-property values such as the rigidity, viscosity, and the like of a material measured by a viscoelastic spectrum meter and physical-property values such as a modulus of direct elasticity (Young's modulus) of a constituting material of a ball measured by a tension tester are used as input data in the simulation. In particular, because the viscoelastic spectrum meter measures the physical-property values of a dynamic strain-applied specimen, the viscoelastic spectrum meter is useful for simulating products made of the viscoelastic material.
However in measurement conducted by using the viscoelastic spectrum meter and the tension tester for measuring the modulus of direct elasticity, a large deformation amount cannot be imparted to the specimen. Thus a maximum strain speed applied to the specimen made of the viscoelastic material at a measuring time is as low as 0.001/s to 1.0/s and a maximum compression strain is also as low as 0.0001 to 0.02.
A product made of the viscoelastic material may deform rapidly and greatly owing to the influence of an external force applied thereto when it is actually used. For example, when a golf ball is hit, a maximum strain speed of a material for the golf ball is as high as 500/s to 5000/s and a maximum compression strain thereof is as large as 0.05-0.50.
As described above, the viscoelastic spectrum meter and the tension tester for measuring the modulus of direct elasticity are incapable of measuring the physical-property values of the viscoelastic material in a state equivalent to a condition where the product made of the viscoelastic material deforms quickly and greatly when it is actually used. Thus the maximum strain speed of the viscoelastic material and its maximum compression strain measured at a simulation time are much different from those measured at the time when the product made of it is actually used. Therefore the conventional simulation method of inputting the physical-property value obtained by using the viscoelastic spectrum meter and the tension tester is incapable of accomplishing an accurate simulation by taking the physical property of the viscoelastic material into consideration.
That is, it is known that the deformation behavior of the viscoelastic material when an impact load is applied thereto is different from that of the viscoelastic material when a static load is applied thereto. That is, the deformation behavior of the viscoelastic material is greatly influenced by a deformation amount or a deformation speed. In particular, when a macromolecular material such as rubber and elastomer is subjected to the impact load, it deforms at a speed as high as several seconds by 10000 or several seconds by 1000 and as greatly as by several tens of percentages in a quantitative respect. There are many viscoelastic materials that deform at such a high speed and in such a large amount. To develop products efficiently, there is a demand for conducting an accurate simulation. More specifically, the performance of a product such the golf ball depends on a dynamic behavior in a condition where it deforms greatly and quickly upon application of an impact thereto when it is hit. The performance of the product also depends on the characteristic of the material thereof. Therefore to develop a product, it is indispensable to conduct an accurate simulation in a condition equivalent to a condition in which the product made of the material is actually used.
Some viscoelastic materials change in the physical properties thereof such as the loss factor, rigidity (modulus of direct elasticity), and the like in dependence on the magnitude of a strain and a strain speed when an external force such as an impact load is applied thereto. That is, the viscoelastic material is diverse in its deformation speed and deformation magnitude. Thus depending on the deformation speed and the deformation magnitude, the physical property of the viscoelastic material has a property that it changes not linearly but nonlinearly. More specifically, as the viscoelastic material is deformed by an external force applied thereto and strained increasingly, the loop area of an S-S (strain-stress) curve increases and the physical properties such as the loss factor thereof change owing to a deformation state (speed and magnitude of deformation) thereof, thus showing nonlinearity in its property. Many viscoelastic materials have a high nonlinearity in their properties. Thus there is a demand for conducting an accurate simulation for a product made of such a viscoelastic material.
However there are no methods capable of accurately expressing a phenomenon that the physical property of the viscoelastic material, for example, its loss factor changes nonlinearly in a high extent in dependence on the deformation speed of and deformation magnitude thereof. Simulations have been hitherto conducted on the assumption that the physical-property value of the viscoelastic material composing the golf ball or the like hardly changes. Consequently the conventional simulation method has a disadvantage that it is incapable of correctly estimating the performance of the product made of the viscoelastic material in an actual use. Thus to estimate the performance of the product, trial manufacture cannot but be made.